This invention relates to thermistor compositions comprising transition metal such as iron, rare earth of the lanthanide series or yttrium and oxygen, including, in particular, thermistors that operate free of significant oxygen dependence, especially in the exhaust gas of internal combustion engines and, accordingly, are suited for use with oxygen sensors such as those derived from titania.
The use of oxygen sensors containing titania that are temperature compensated by a separate chip is illustrated in commonly assigned U.S. Ser. No. 839,704, now U.S. Pat. No. 4,151,503 (Temperature Compensated Resistive Exhaust Gas Sensor Construction) filed in name of Cermak et al on Oct. 5, 1977, which is hereby incorporated herein by reference, especially including those portions comprehending the use of oxygen sensors and thermal compensators therefor in feedback fuel control systems of internal combustion engines. Previous suggestions for providing such temperature compensation at least partially independent of oxygen partial pressure, made, for example, in the next above application, include densifying a ceramic as titania (see, also, commonly assigned U.S. Ser. No. 839,700, now abandoned (Titania Thermistor and Method for Fabricating) filed in name of Merchant et al. on Oct. 5, 1977) so as to minimize response to oxygen changes under exhaust gas conditions as well as a suggestion of coating a ceramic with, for example, glass (see, also, commonly assigned U.S. Ser. No. 839,705 (Encapsulated Titania Thermistor and Method of Fabrication) filed in name of Heiney et al. on Oct. 5, 1977) so as to provide a barrier to oxygen.